1. Field of the Invention
The present invention relates to a flyback switching power supply and control method thereof, and more particularly, to a flyback switching power supply and related control method capable of regulating an operation frequency based on a current regulation mechanism.
2. Description of the Prior Art
Along with well-known advantages of high efficiency, low power consumption, small size and light weight, the flyback switching power supply has been widely employed as a power converter in various electronic products. Please refer to FIG. 1, which is a schematic diagram showing a prior-art flyback switching power supply 100. Rectifier 102 and filter capacitor 105 are put in use for performing rectification and filter operations on an alternating input voltage Vac, provided by alternating power supply 101, so as to generate an input voltage Vin furnished to transformer 120. Transformer 120 comprises a primary winding 121 for receiving input voltage Vin, a secondary winding 122 for generating a preliminary output voltage, and an auxiliary winding 123. Rectify/filter circuit 170 is utilized for performing rectification and filter operations on the preliminary output voltage for generating an output voltage forwarded to load 195 and feedback circuit 140. Feedback circuit 140 functions to convert the output signal into a feedback signal furnished backwards to switch control circuit 130.
Power generation circuit 190 is used to generate a power voltage Vcc for powering switch control circuit 130 based on an induced current generated by auxiliary winding 123. In general, the operation frequency of control signal Sc is mainly adjusted by switch control circuit 130 based on a frequency setting current If flowing through the current setting resistor Rx externally connected. However, the operation frequency is normally preset to be a fixed value in that the current setting resistor Rx is mostly set to be a fixed resistor as shown in FIG. 1.